Air filter restriction indicating devices are known from, for example, U.S. Pat. No. 4,445,456; U.S. Pat. No. 5,850,283; U.S. Pat. No, 6,327,902; and PCT International Publication Number WO-97/18027. While these devices appear to be suitable for their intended purpose, it would be desirable to provide a device which is mechanically simpler, less costly to manufacture, and/or more easily integrated into existing air filter housing side walls.